The major goals of the proposed research are: 1) to determine the mechanism by which botulinum toxin blocks transmitter release from cholinergic nerves, and 2) to use botulinum toxin as a pharmacological tool to study cetain aspects of cholinergic transmission. In order to accomplish the final goal, the applicant proposes to isolate and characterize types A and B toxins. In addition, the "binding" and "lytic" fragments of these toxins will be isolated. Antibodies will be prepared both to the intact toxins and to the individual fragments. The toxins, their fragments and their antibodies will then be used in: a) pharmacological studies aimed at determining the mechanism of action of botulinum toxin, b) histological studies intended to localize the toxin at the neuromuscular junction, and c) biochemical studies aimed at identifying and isolating the receptor(s) for botulinum toxin. In order to accomplish the second goal, the applicant proposes to use botulinum toxin as a research tool to analyze autonomic regulation of the mammalian heart. In particular, the applicant will attempt to: a) use the toxin as a histological marker to localize and quantify postganglionic parasympathetic nerve endings, b) use the toxin to produce discrete interruption of parasympathetic nerve function, and c) use the toxin to determine whether denervation supersensitivity develops between postganglionic parasympathetic nerves and the structures they innervate.